Conventionally, an HDD (Hard Disk Drive) device (which will be referred to as a memory device hereinafter) having an encrypting function encrypts data by using a previously held encryption key and stores obtained encrypted data. This type of memory device sets the previously held encryption key as a decryption key when password authentication of a user who has an access right has succeeded, and decrypts encrypted data by using this decryption key to output resultant data. As described above, the conventional memory device can output correct data to a user who has an access right.
However, when a conventional memory device is taken out to an external system environment by a user who has an access right with encrypted data being stored, decrypted data may possibly be leaked because of success of password authentication.
Further, since a small memory device can be easily taken out, theft is apt to occur, and decrypted data can be leaked when a password is broken after a theft. Therefore, to avoid data leakage at the time of a theft, data must be assuredly nullified at a place that the memory device is brought out to.
As described above, the conventional memory device has a desire of nullification of stored data irrespective of an access right of a user when accessed from an environment different from a useable system environment.